If I were to plant a sweet cherry tree would I have to plant 2 trees in order for pollination or will one tree self pollinate to get cherrys?

That would depend on which variety of sweet cherry that you have. What is quoted below is from the following site. Pollination of Tree Fruits

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Sour and Sweet Cherry
All sour cherries are self-fruitful. These include Montmorency, North Star, Montmore, Meteor, English Morello, Early Richmond, Hansen Bush Cherry and Nanking. Index, Lapins, Stella and Sweetheart are self-fruitful sweet cherries. All other varieties are self-unfruitful. There are several varieties that are cross-unfruitful. For example, Bing, Lambert and Royal Ann (Napoleon) will not pollinate each other. Move bees into orchards on the first day of bloom.

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